With the recent influx of Spanish M1916s into the collectors market,
we will revisit some of the general differences between rifles chambered in 7x57 and 7.62x51mm NATO.

The buttstock for the 7.62 rifle (top) will typically have the addition of a crossbolt for added strength.
In addition, the trigger guard will be modified to a lock screw configuration.

While both will have the side mounted sling (solid metal pinned version shown), the 7.62 rifle (right) will have the buttplate bottom cupped. Some rifles may have a cutout with screwed in sling swivel.

With the handguard removed, it is easy to see indications of the conversion to 7.62x51. Other than re-boring, the shortening of the chamber by 6mm is obvious due to the setback at the receiver (bottom). Naturally, this precludes the hanguards between the two rifles being directly interchangeable. You will also note that, due to the change in ballistics, the rear sight has had the original "3" overstruck with a "2".

Depending on the end user, the rifle may have the Guardia Civil "Falangist" crest added.

You may also have an un-crested NATO conversion easily identified by the "OT" (Organización del Tratado del Atlántico Norte).

You got me looking at my 1916 rifle. Mine is stamped with the caliber of 7.52, but has the cross bolt. Sight #3 position still unmarked in anyway. Took off the hand guard and the barrel is set back. Any idea about the caliber stamp???

It has a Z prefix on the assy number, serial has no prefix. I did put a ball gauge in the barrel, came out around .302, which excludes the rifling depth. A 308 brass fit perfectly and extracted, so I guess it's a fluke with the caliber stamp.

The rear sight is different from the 2 known types. It starts at 1 and has not been renumbered in any way. If I remember correctly the RF number has something to do with the differences from 7mm and 7.62 1916 carbines. When I have more time, I'll have to do the research again to come up with what I found out years ago.
Nice civil guard crest on the one above. I looked for a time but couldn't find one in 7mm. Were all the civil guard ones converted to 7.62?

I just looked at my Spanish M1916, so here's another odd-ball for you! Characteristics of it compared to the ones originally listed.

Left side of receiver CAL 762, then the SN A 9850 (What is strange is you can see the ghosting of the previous SN which is also 9850 can't tell if it was preceded by an A). Receiver, bolt (Which has a bent handle), floor plate, and barrel band SN's match.

Right side of receiver the number 28942.

The rear sight there is a 3 on the slide and a 3 of the right side of the ramp, no over-stamping of a 2.

Stock has a cross bolt.

The trigger guard is a standard guard not modified for the lock screw, even though the screw on the TG has divots in it to be used with a lock screw.

There is no Guardia Civil "Falangist" crest or OT number on the rifle.

The butt plate is not cupped.

The side mounted sling mount on the butt stock is the solid metal pinned version.

Thumb cutout on left side rail.

Gas escape hole on left side of receiver.

Attachments

The only overall shot of the rifle in my files!

You can see the numbers stamped on the right side of the receiver, meaning unknown to me!

If you open in a new tab and zoom in, you can just make out the CAL 762 stamp, the serial number and ghosting of the previous SN between them!

I just looked at my Spanish M1916, so here's another odd-ball for you! Characteristics of it compared to the ones originally listed.

Left side of receiver CAL 762, then the SN A 9850 (What is strange is you can see the ghosting of the previous SN which is also 9850 can't tell if it was preceded by an A). Receiver, bolt (Which has a bent handle), floor plate, and barrel band SN's match.

Right side of receiver the number 28942.

The rear sight there is a 3 on the slide and a 3 of the right side of the ramp, no over-stamping of a 2.

Stock has a cross bolt.

The trigger guard is a standard guard not modified for the lock screw, even though the screw on the TG has divots in it to be used with a lock screw.

There is no Guardia Civil "Falangist" crest or OT number on the rifle.

The butt plate is not cupped.

The side mounted sling mount on the butt stock is the solid metal pinned version.

Thumb cutout on left side rail.

Gas escape hole on left side of receiver.

To a certain level, it's a typical, though incomplete, conversion. It still has the 7x57 butt, TG, and sights, apparently. If these rifles could talk. Purpose made M1916s, rebuilt M1893s, captured arms from SCW, etc.
I would love to see more members post their variations.